1. Field of the Invention
The present invention relates to a motor driving device. More particularly, the present invention relates to a two-phase half-wave motor driving device that drives a motor by energizing a coil of a first phase (a first-phase coil) and a coil of a second phase (a second-phase coil) provided in the motor in one direction alternately, and to a sensorless motor driving device that drives a motor by controlling energization of coils of individual phases provided in the motor according to the result of detecting the position of a rotor of the motor without using an external sensor such as a hole element.
2. Description of the Prior Art
FIG. 11 shows a block diagram of a conventional, common two-phase half-wave motor driving device 100xe2x80x2. A hole element H is arranged so as to face a rotor of a motor M. A comparator 101 outputs a binary signal that represents the relationship in magnitude between the voltages output from both ends of the hole element H. A commutation portion 102, according to the binary signal output from the comparator portion 101, decides which of two transistors T1 and T2, which together constitute an output portion 104, to turn on, and outputs a logic signal to be fed to the gates of the transistors T1 and T2.
The signal output from the commutation portion 102 is converted, by a pre-drive portion 103, to a level high enough to turn on and off the transistors T1 and T2, and is then fed to the gates of the transistors T1 and T2. In the output portion 104, an n-channel MOS field-effect transistor T1 is connected between one end of a first-phase coil L1, of which the other end is connected to a drive voltage VM for the motor M, and ground. Moreover, an n-channel MOS field-effect transistor T2 is connected between one end of a second-phase coil L2, of which the other end is connected to the drive voltage VM for the motor M, and ground.
The signal output from the hole element H represents the position of the rotor. Thus, with the circuit configuration described above, it is possible to switch which phase to energize with appropriate timing according to the position of the rotor, and thereby rotate the rotor smoothly.
The problem with this conventional, common two-phase half-wave motor driving device is that it requires an external sensor (hole element) to detect the position of the rotor. This has been hindering cost reduction and miniaturization.
An object of the present intention is to provide a two-phase half-wave motor driving device that helps promote cost reduction and miniaturization.
Another object of the present invention is to provide a sensorless motor driving device that, despite having a simple circuit configuration, prevents reverse rotation of a motor.
To achieve the above objects, according to one aspect of the present invention, in a motor driving device for driving a motor by energizing a coil of a first phase and a coil of a second phase provided in the motor in one direction alternately, which phase to energize is switched according to a back electromotive force appearing in the coil of each phase of the motor as a rotor of the motor rotates.
This circuit configuration eliminates the need for an external sensor for detecting the position of the rotor, and thus helps promote cost reduction and miniaturization.
Here, the back electromotive force that appears in the coil of each phase as the rotor rotates has a sinusoidal waveform that is synchronous with the rotation of the motor, and becomes equal to zero when the rotor is at an electrically stationary point. This makes it possible to detect the position of the rotor according to the back electromotive force appearing in the coil of each phase. Accordingly, for example, by switching which phase to energize when the back electromotive force appearing in the coil of the phase that is not being energized as the rotor rotates crosses a threshold level, it is possible to rotate the rotor as smoothly as when an external sensor is used to detect the position of the rotor.
In a case where which phase to energize is switched when the back electromotive force appearing in the coil of the phase that is not being energized as the rotor rotates crosses a threshold level, it is preferable that the threshold level be so set that the voltage at the open end of the coil of the phase that is not being energized is not higher than zero if this end is on the current outflow side when this phase is energized, and that the voltage at the open end of the coil of the phase that is not being energized is not lower than zero if this end is on the current inflow side when this phase is energized. This makes it possible to prevent the motor""s failure to rotate resulting from spike noise that appears in the coil of each phase when the coil of each phase is switched from an energized state to a de-energized state.
Which phase to energize may be switched by first stopping energizing the coil of the phase that has been energized thus far, and then starting energizing the coil of the phase that has not been energized thus far. This circuit configuration prevents the first and second phases from being energized simultaneously when which phase to energize is switched, and thus helps reduce power consumption and ensure efficient rotation of the motor.
According to another aspect of the present invention, in a motor driving device for driving a motor by controlling energization of coils of individual phases of the motor according to the result of detecting the position of a rotor of the motor without using an external sensor, the motor is started by first bringing the rotor to rest in a particular position and then energizing the coil of a particular phase.
This circuit configuration permits the motor to be started always in the same rotation direction, and thus prevents reverse rotation of the motor.
Specifically, in a case where the motor driving device is used to drive a motor that is so designed that its rotor does not come to rest at an electrically stationary point, the rotor is brought to rest in the particular position by first energizing the coil of a particular phase and then de-energizing the coils of all phases.